Dear Shell:
Sorry I can't answer your question for you, but if you return to the defra site there's an email address you can write to.
This subject is of particular interest to me. We moved from South Dakota to Paris, France (Feb. 2004). Before we left I got all the proper French forms filled out, and my dogs were thoroughly gone over... and poked with necessary shots. Well, now that we're looking to move to the UK.... I've sort of had to start from scratch. The "biggest" thing that will set you back is the "blood test and wait 6 months" deal. I should think you would be able to apply for the UK's Pet Passport, from the states. Keep in mind the UK's pet import rules are basically that standard by which the rest of the EU is trying to come into conformity with..... or so it seems. France is continually changing their rules and laws.
We're 2 months into our 6 month wait.... from the time the blood tests were done.
Best of luck, and congrats on the engagement.
PitterPat